Surface Ozone (O3), also called Troposheric Ozone, is a critical atmospheric species that drives much of tropospheric photochemistry.
It regulates the oxidation capacity of the troposphere, influencing background levels of trace chemicals. Ozone is also a strong greenhouse gas, and is the third most important contributor to greenhouse radiative forcing behind CO2 and CH4.

Ozone is produced in the troposphere by photochemical oxidation of CO, CH4 and non-methane volatile organic carbons (NMVOCs) in the presence of NOx. Stratosphere-troposphere exchange is another source of ozone to the troposphere. Loss of tropospheric ozone takes place through chemical reactions and dry deposition.
Ozone is a key trace gas for both the chemistry and radiative balance of the troposphere, and is the principal pollutant associated with photochemical smog.

The ESRL Global Monitoring Division has been measuring surface ozone at several global locations starting at Barrow, Alaska and Mauna Loa, Hawaii in 1973. The map and table below show the locations of surface ozone measurements.